The present invention relates to the monitoring of temperature and, more particularly, the measuring of temperature distributions within electrical equipment.
In order to protect electrical equipment from being damaged by localized overheating conditions, it is important that the temperature of internal components of the equipment be continually monitored. However, conventional temperature measuring techniques can be adversely affected by electrical fields that exist within the equipment being monitored and, in some situations, it is difficult to position conventional transducers within the equipment because of spatial restrictions.
The advent of fiber optics has partially solved these problems by providing a lightweight, nonconductive means for conveying temperature transducer signals from within the electrical equipment to remotely located monitoring devices. However, present measuring techniques which utilize fiber optics still typically require a transducer or light source to be located within the electrical equipment.
The distinction between the present invention and most known methods which utilize optical fibers to measure temperature is that conventional techniques use optical fibers to transmit signals from temperature transducers or light sources whereas the optical fibers of the present invention serve as both the transducers which generate temperature related signals and the means for transmitting the signals to a remote receiver. U.S. Pat. No. 4,203,326 issued to Gottlieb, et al on May 20, 1980 and U.S. Pat. No. 4,151,747 issued to Gottlieb, et al on May 1, 1979 both utilize external light sources to measure temperature as a function of its effect on the light transmission capability of optical fibers.
Implementation of the present invention requires only that the optical fibers be disposed within the environment whose temperature is being measured. The optical fibers are arranged in a bundle, or cable. The cable is extended into the environment being monitored, such as the interior of an electrical generator, with proper fastening means to insure the cable's stationary position. Prior to sealing the environment, if that's necessary, the locations on the cable which are proximate various selected internal components of the generator are recorded as a function of their distance from one end of the cable in order that measured temperatures can later be related to cable position and, thus, to specific internal components.
One end of the cable, having been extended from the environment being monitored, is connected to equipment that is capable of measuring the thermal radiation emanating from each of the optical fibers in the cable. The present invention utilizes the physical characteristic of the optical fibers which enables them to generate spontaneous thermal radiation in response to, and as a function of, their temperature. Since the cable and its fibers will tend to achieve a temperature equilibrium with the surrounding environment, a temperature distribution of the surrounding environment can effectively be mapped from the temperature distribution of the cable in accordance with the present invention.
The number of fibers required to be included in the cable is directly proportional to the accuracy and resolution desired in the ability to pinpoint locations along the cable where a temperature to be measured exists and also to its capability to precisely measure the magnitude of the temperature at those locations.
Using the equipment described above, each fiber can be mathematically divided into a predetermined number of segments or zones. This number of zones is the same for each fiber and is equal to the number of fibers in the bundle. By requiring each fiber of the cable to have an absorption constant which is distinct from all other fibers in the cable, each of these fiber segments or zones can be assigned a variable that represents its unknown contribution to the sum total of radiation emanating from the fiber's end and the resulting simultaneous equations will have a unique solution which gives the temperature for each of the above described segments. It should be apparent that the average length of the zones is equal to the length of the cable divided by the number of fibers in the cable.
The present invention provides a means for monitoring the temperature variations along a cable of optical fibers without the need for any other transducers, light sources or transmitting equipment within the environment being monitored.